Even though there has been considerable study of alternative electrochemical systems, the lead-acid battery is still the battery of choice for general purposes, such as starting a vehicle, boat or airplane engine, emergency lighting, electric vehicle motive power, energy buffer storage for solar-electric energy, and field hardware, both industrial and military. These batteries may be periodically charged from a generator.
The conventional lead-acid battery is a multi-cell structure. Each cell comprises a set of vertical positive and negative plates formed of lead-acid alloy grids containing layers of electrochemically active pastes. The paste on the positive plate when charged comprises lead dioxide, which is the positive acting material, and the negative plate contains a negative active material such as sponge lead. An acid electrolyte, based on sulfuric acid, is interposed between the positive and negative plates.
Lead-acid batteries are inherently heavy due to use of the heavy metal lead in constructing the plates. Modern attempts to produce light-weight lead-acid batteries, especially in the aircraft, electric car and vehicle fields, have placed their emphasis on producing thinner plates from lighter weight materials used in place of and in combination with lead. The thinner plates allow the use of more plates for a given volume, thus increasing the power density.
Higher voltages are provided in a bipolar battery including bipolar plates capable of through-plate conduction to serially connected electrodes or cells. The bipolar plates must be impervious to electrolyte and be electrically conductive to provide a serial connection between electrodes.
U.S. Pat. Nos. 4,275,130; 4,353,969; 4,405,697; 4,539,268; 4,507,372; 4,542,082; 4,510,219; and 4,547,443 relate to various aspects of lead-acid batteries. Certain of these patents discuss various aspects of bipolar plates.
One problem which has presented itself, particularly with regard to bipolar plates, is maintaining the integrity of the plate as the battery is repeatedly cycled between charge and discharge modes. For example, in certain previous bipolar plate configurations, the positive active electrode material, which is originally adhered to an electrically conductive matrix, separates from the matrix after repeated charge/discharge cycles. Also, such charge/discharge cycles tend to cause portions of the positive active electrode material to shed, drop or flake off the mass of this material. Both of these phenomena reduce the effectiveness and effective life of the battery containing such plates.
Commonly assigned U.S. patent applications Ser. Nos. 843,047, filed Mar. 24, 1986, now U.S. Pat. No. 4,713,306, and 843,053, filed Mar. 24, 1986, now U.S. Pat. No. 4,708,918, disclose improved lead-acid battery elements. The disclosure of each of these applications is incorporated in its entirety herein by reference. However, neither of these applications specifically addresses the problems discussed in the preceding paragraph.